STRUCTURAL ANALYSIS OF THE TABLEROCK THRUST SHEET, GRANDFATHER MOUNTAIN WINDOW, NORTHWESTERN NORTH CAROLINA: EMPLACEMENT KINEMATICS OF A LARGE HORSE IN A MAJOR THRUST SYSTEM

The Tablerock thrust sheet (TR) is exposed along the southwestern margin of Grandfather Mountain window in northwestern North Carolina, where it separates basement and cover rocks inside the window from basement thrust sheets of the overriding Blue Ridge-Piedmont megathrust sheet. It is a complex of footwall-derived horses of rifted-margin metasedimentary rocks, including Lower Cambrian Chilhowee Group quartzite and phyllite, and Shady Dolomite. While the TR resides between the roof thrust and imbricates of the now-eroded antiform duplex of the window, previous work by Bryant & Reed, Boyer, and others indicate it may not be part of the thrust stack beneath it. Penetrative deformation within the TR is defined by bedding-parallel foliation (S₁); a prominent NW-trending mineral lineation (L₁); mesoscale NW-trending tight to isoclinal and sheath folds (F₁); and NE-trending/NW-vergent crenulations (F₂). NE-trending mesoscale open folds overprint these fabric elements, and likely represent third-generation folds (F₃). Centimeter-scale intrafolial folds with rootless hinges or attenuated limbs are common, and confirm transposition has occurred; bedding and sheared quartz veins are also rotated into the dominant foliation, and reflect top-to-NW transport. Although metamorphic grade is chlorite-biotite, NW-trending mesoscale sheath folds are locally well-developed; map-scale sheath folds may also exist, as indicated by outcrop patterns on Bryant & Reed’s 1970 map. Parallel alignment of NW-trending tight folds and the L₁ lineation is consistent with development of NW-trending sheath folds, and suggests transport of the TR was non-rotational; the trend of L₁ therefore defines the transport direction, while NW-trending tight to isoclinal and sheath folds may represent parasitic folds or minor culminations related to NW-verging macroscopic sheath folds. Mesofabric analysis suggests the TR formed and moved into the thrust stack independently of the antiformal duplex beneath it.